Theists: What is the most compelling argument you have heard for Atheism?

[masterofpuppets]

I did some reading on M-theory. First, there is not one bit of physical evidence for it. Second, it posits as many as 10^500 different possible membranes (parallel universes) that could be right next to us. With that many universes--each with a different possibility of constants, it does not address the fine-tuning issue of why ours is the way it is. Third, it is not clear that whatever created the 'cosmic landscape' (multiverse?) would not have to have been finely tuned to create universes with laws and structure (kicking the can upstairs). Fourth, since it is very much in question whether the theory can ever be tested, isn't it just philosophy and not science?

You seem to be having a discussion with yourself.  I simply disputed your claim  that there is no debate whether the values of physical constants can take on different values.   Far from there being no debate about it, I showed that the quest for a unified theory which would explain all the physical constants is very much alive.  Whether it's M-theory or another, the idea that there is no debate as to whether these constants can take on different values is rubbish.  You rule out chance for irrational reasons, and you try to rule out necessity by simply declaring that nobody takes the possibility seriously, despite the fact that they do.  Your chance, necessity or design trilemma is less settled than you will admit.  Whether it's M-theory or not, the notion that the physical constants are the way they are for naturalistic reasons is not something you can rule out at this stage.

As Sean Carroll explains in his debate with WLC, physicists have built viable models where the probability of universes having "suitable" constants approaches 1, and these are actually scientific explanations that fit the data and can make predictions. "God did it" is just philosophical nonsense with no explanatory or predictive power. I think we're actually all tending to the conclusion that no gods exist.